The present disclosure is directed to a combustion system. In particular, the present disclosure is directed to an oxy/fuel combustion system.
The conversion of boilers and process heaters from air/fuel to oxy/fuel operation for CO2 capture and/or purification represents a major modification to a mature technology. Much of the technical discussion surrounding effects introduced into the performance of these boilers and heaters has focused on the distribution of heat transfer between, for example, radiant and convective exchange, and its effect on process efficiency and component life.
Many large boilers and heaters operate with dozens of burners. These burners impart mixing and momentum to reactants that largely define factors such as flame length, shape, luminosity and efficiency of carbon burn out. These performance factors are finely tuned by process engineers and operators over years of operation to facilitate process conditions enabling component life and process efficiency to be increased. It is known, however that, due largely to differences in emissivity and heat capacity between nitrogen and carbon dioxide, the reactant flow rates for oxy/fuel operation using synthetic air (CO2/O2) may be lower than for equivalent air/fuel firing rates. Since the number of burner designs used in current commercial practice is very large, it is not practical to attempt an optimization of each burner design. It is more practical to provide a device that can be fitted onto existing or future burners to provide adjustability to the flame characteristics as they are encountered during boiler and process heater operation. It is accordingly the object of this disclosure to describe a device and method of operation of oxy-fuel burners used in boilers and process heaters that allows for this adjustability to occur.
At fixed fuel firing rate, recycling of flue gas may permit process operators to optimize heat exchange within the system. Generally, the proportion of flue gas recycle to oxygen flow rate results in a mixed concentration of O2 in CO2 of between 25 and 30 mol % for air/fuel firing. The level is different when considering matching of flame temperature than it is for matching of heat exchange characteristics, and it is also fuel dependent. Moreover, the relative importance of burner flame momentum in this optimization is essentially unknown.
U.S. Pat. No. 5,256,058 discloses an oxy-fuel burner that employs a precombustor between a burner and a process furnace. U.S. Pat. No. 5,199,866 discloses an adjustable oxy-fuel burner. The disclosure of these U.S. Patents is hereby incorporated by reference.
There is a need in this art for an oxy-fuel combustion system and method for its usage that can employ recycled flue-gas (RFG) in a burner that can produce a flame having desirable properties.